Reduced IMU power consumption in a wearable device

Abstract

Systems and methods for detecting touch events with an accelerometer are disclosed. In one aspect, a method includes measuring first accelerometer data at a first rate, detecting a first touch event based on the first accelerometer data, in response to detecting the first touch event, measuring second accelerometer data at a second rate, determining whether a second touch event is detected based on the second accelerometer data, measuring third accelerometer data at the first rate in response to an absence of the second touch event being detecting in the second accelerometer data over a predetermined threshold period of time.

What is claimed is: 
     
       1. A method of operating an electronic device, the method comprising:
 operating an inertial measurement unit (IMU) of the electronic device in a first state of a plurality of states, the first state enabling the IMU to detect presence of motion without determining direction of the motion; 
 detecting motion of the electronic device; 
 in response to detecting the motion, transitioning the IMU to a second state of the plurality of states, the second state enabling the IMU to detect directional information relating to motion; 
 detecting a first tap event of the electronic device while the IMU operates in the second state; 
 in response to detecting the first tap event, transitioning the IMU to a third state of the plurality of states, the third state stores a number of acceleration measurements in a queue; and 
 transitioning the IMU back to the second state when a second tap event is not detected after a threshold amount of time while the IMU operates in the third state. 
 
     
     
       2. The method of  claim 1 , further comprising:
 detecting a third tap event while the IMU operates in the third state; and 
 performing a predetermined action in response to detecting the third tap event. 
 
     
     
       3. The method of  claim 2 , wherein the predetermined action is displaying, on an electronic display, a battery status indication. 
     
     
       4. The method of  claim 1 , further comprising:
 changing a measurement rate of the IMU in response to an absence of touch events being detected over the threshold amount of time. 
 
     
     
       5. The method of  claim 4 , wherein the IMU consumes less power when operating in the first state than the second state, and the IMU consumes less power when operating at the second state than at the third state. 
     
     
       6. The method of  claim 1 , wherein the first tap event is detected by invoking a trained classifier to detect the first tap event based on acceleration data captured by the IMU. 
     
     
       7. The method of  claim 6 , wherein invoking the trained classifier comprises comparing filter responses to the acceleration data to filter responses of training acceleration data. 
     
     
       8. The method of  claim 7 , wherein comparing filter responses to the acceleration data to filter responses of training acceleration data comprises comparing filter responses to the acceleration data to filter responses of training acceleration data indicating a touch event, and comparing the filter responses to the acceleration data to filter responses of training acceleration data that does not indicate a touch event. 
     
     
       9. An electronic device comprising:
 one or more processors configured to perform operations comprising:
 operating an inertial measurement unit (IMU) of the electronic device in a first state of a plurality of states, the first state enabling the IMU to detect presence of motion without determining direction of the motion; 
 detecting motion of the electronic device; 
 in response to detecting the motion, transitioning the IMU to a second state of the plurality of states, the second state enabling the IMU to detect directional information relating to motion; 
 detecting a first tap event of the electronic device while the IMU operates in the second state; 
 in response to detecting the first tap event, transitioning the IMU to a third state of the plurality of states, the third state stores a number of acceleration measurements in a queue; and 
 transitioning the IMU back to the second state when a second tap event is not detected after a threshold amount of time while the IMU operates in the third state. 
 
 
     
     
       10. The electronic device of  claim 9 , further comprising operations for:
 detecting a third tap event while the IMU operates in the third state; and 
 performing a predetermined action in response to detecting the third tap event. 
 
     
     
       11. The electronic device of  claim 10 , wherein the predetermined action is displaying, on an electronic display, a battery status indication. 
     
     
       12. The electronic device of  claim 9 , further comprising operations for:
 changing a measurement rate of the IMU in response to an absence of touch events being detected over the threshold amount of time. 
 
     
     
       13. The electronic device of  claim 12 , wherein the IMU consumes less power when operating in the first state than the second state, and the IMU consumes less power when operating at the second state than at the third state. 
     
     
       14. The electronic device of  claim 9 , wherein the first tap event is detected by invoking a trained classifier to detect the first tap event based on acceleration data captured by the IMU. 
     
     
       15. The electronic device of  claim 14 , wherein invoking the trained classifier comprises comparing filter responses to the acceleration data to filter responses of training acceleration data. 
     
     
       16. The electronic device of  claim 15 , wherein comparing filter responses to the acceleration data to filter responses of training acceleration data comprises comparing filter responses to the acceleration data to filter responses of training acceleration data indicating a touch event, and comparing the filter responses to the acceleration data to filter responses of training acceleration data that does not indicate a touch event. 
     
     
       17. A non-transitory computer readable storage medium that stores instructions that when executed, cause a hardware processor to perform operations comprising:
 operating an inertial measurement unit (IMU) of an electronic device in a first state of a plurality of states, the first state enabling the IMU to detect presence of motion without determining direction of the motion; 
 detecting motion of the electronic device; 
 in response to detecting the motion, transitioning the IMU to a second state of the plurality of states, the second state enabling the IMU to detect directional information relating to motion; 
 detecting a first tap event of the electronic device while the IMU operates in the second state; 
 in response to detecting the first tap event, transitioning the IMU to a third state of the plurality of states, the third state stores a number of acceleration measurements in a queue; and 
 transitioning the IMU back to the second state when a second tap event is not detected after a threshold amount of time while the IMU operates in the third state. 
 
     
     
       18. The non-transitory computer readable storage medium of  claim 17 , further comprising operations for:
 detecting a third tap event while the IMU operates in the third state; and 
 performing a predetermined action in response to detecting the third tap event. 
 
     
     
       19. The non-transitory computer readable storage medium of  claim 18 , wherein the predetermined action is displaying, on an electronic display, a battery status indication. 
     
     
       20. The non-transitory computer readable storage medium of  claim 17 , further comprising operations for:
 changing a measurement rate of the IMU in response to an absence of touch events being detected over the threshold amount of time.